Method of modeling of faulting and fracturing in the earth

Abstract

A computer implemented method for modeling of faulting and fracturing uses “small scale rules” to produce large-scale results. One part of the method is a user interface for inputting deformations, preexisting faults and fractures, and material rock properties. The second part of the software is the code that solves the motion of each point or node in the subsurface volume defined by the user interface. The model may be defined in one of three modes: an aerial mode, in which the model is 2-dimensional with the material and a substrate on a horizontal plane; a cross-sectional mode similar to the aerial mode except that the nodes are in a vertical cross section and gravity is included in the model; and a 3-D model that is an extension into a third dimension of the 2-D model and deformation may be applied to the bottom and four sides of the material region.A modified over-relaxation approach, wherein the over-relaxation is concentrated in those nodes where the greatest movement occurs, is used to solve for the deformation. This significantly speeds up the computation time. The model is “conditioned” to increase the likelihood that the deformation pattern resulting from the simulation of the deformation will at least duplicate an observed large-scale deformation. As an aid to the simulation, an “anticipate” step provides a quick solution to the deformation without including the effects of faulting.

Description

CROSS REFERENCES TO RELATED APPLICATIONS[0001]This application is a continuation-in-part of U.S. patent application Ser. No. 09 / 542,307 filed on Apr. 4, 2000, now U.S. Pat. No. 6,370,491.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The invention relates to a method for forward modeling the spatial distribution faults and fractures in a geologic formation.[0004]2. Background of the Invention[0005]The prediction of faulting and fracturing is very important in oil and gas exploration and production. Seismic data is often used to find faults that bound or delineate hydrocarbon reservoirs. However, due to the limited resolution of seismic data, the details of the faulting in the subsurface may not be determinable.[0006]Knowledge of the distribution of the fractures in a geologic formation is of great importance first for optimizing the location and the spacing between the wells that are to be drilled through an oil formation. Furthermore, the geometry of the fracture n...

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Benefits of technology

[0018]The computational method used in solving for the deformation is a modified over-relaxation approach. In the basic over-relaxation method, equilibrium is reached by moving each node a distance proportional to the force acting on the node. The constant of proportionality is called the over-relaxation constant and optimal methods for selecting it are known. In each relaxation cycle, each node is moved and the relaxation cycles repeated until no node is moved further than a threshold distance, which is called the relaxation threshold. In the present invention, the over-relaxation is concentrated in those nodes where the greatest movement occurs. This significantly speeds up the computation time.

[0019]A novel aspect of the invention is the conditioning of the model. In the real world, the interpretation of the subsurface structure starts with observations of large scale fracturing and faulting. In one aspect of the invention, based upon the observed large-scale deformations, the user derives an initial geometry of the unfaulted material. Since it is clearly desirable that the end result of applying stresses to the model should at least duplicate the observed large-scale deformations, the model is weakened at the reconstructed fault positions so that upon application of the stresses, there will be a predisposition to produce the observed large-scale fractures and faults. The conditioning step is made easier in the present invention by use of the graphical user interface.

Problems solved by technology

This significantly speeds up the computation time.

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